Volumes of production

Explosive forming can be used for one-off art projects such as sculptures and installations, but it is equally suitable for mass-production of industrial components. In former East Germany it was used to make hundreds of thousands of cardan axles for heavy trucks.

Unit price vs. capital investment

If conventional pressing or spinning can be used, they would usually be cheaper, but relatively low tooling costs and the ability to manufacture complex shapes can make explosive forming the best option available.

Speed

Varies enormously depending on the size and complexity of the shape. Sometimes it is possible to manufacture twenty small parts in one explosion, while larger, more intricate shapes can require up to six explosions over three days. Even a single explosion is quite time-consuming, however, due to the lengthy setup time (amounting to over an hour per explosion).

Surface

Surface quality is generally extremely good. It is possible to form grade 2G (chemically polished) stainless steel without damaging even the protective foil, producing parts with a perfect mirror finish.

Types/complexity of shape

Ideal for forming complex shapes with seamless cavities.

Scale

Specific manufacturers can form sheets of nickel up to an incredible thickness of ½ inch, with lengths of up to 30 feet. Larger sheets are only achievable by welding sheets together.

Tolerances

Able to maintain precise tolerances.

Relevant materials

The process is not restricted to soft metals such as aluminum, but embraces all metals, including titanium, iron, and nickel alloys.

Typical products

Large architectural components and panels, and parts for the aerospace and automotive industries.

Similar methods

Superforming aluminum (p.70) and inflating metal (p.76).

Sustainability issues

Relatively slow cycle times coupled with intensive energy consumption hinder the use of this process for sustainable manufacture. In fact, some larger forms can require several explosions to deform fully, which further increases energy use. Harmful substances are used to create the explosive chemical reaction and need to be cleaned before disposal.

Further information

www.3dmetalforming.com

Superforming Aluminum

including cavity, bubble, back-pressure, and diaphragm forming

Product	MN01 bike
Designer	Marc Newson
Frame builder	Toby Louis-Jensen
Materials	aluminum
Manufacturer	Superform Aluminium
Country	UK
Date	1999

This bike is a good example of the transfer of industrial manufacturing processes into consumer products by experimental projects. The text embossed onto the frame also illustrates the detail that is achievable.

The process of heating a sheet of plastic, draping it over a mold, and sucking the air out has been in use for some time (see thermoforming, p.64). However, as the speed of the development of new materials increases, more technologies overlap when it comes to both materials and processes. Superforming involves such an overlap, since it brings traditional vacuum forming with plastic to aluminum alloys. The process is achieved through four main methods: cavity forming, bubble forming, back-pressure forming, and diaphragm forming, each suited to specific applications. The common element in all these methods is the heating of an aluminum sheet to 840–930°F in a pressurized forming oven, and then forcing it over, or into, a single surface tool to create a complex three-dimensional shape.

In the cavity method, air pressure forces the sheet up into the tool in a process that can be described as “reverse vacuum forming.” According to the manufacturers, this process is ideal for forming large, complex parts such as automotive body panels.

In bubble forming, the air pressure forces the material into a bubble. A mold is then pushed up into the bubble and air pressure is applied from the top, which forces the material to conform to the shape of the mold. Bubble forming is suitable for deep and relatively complex moldings that are difficult to achieve with the other super-forming processes.

Back-pressure forming uses pressure from both the top and bottom surfaces of the mold to maintain the integrity of the sheet and allow for the forming of difficult alloys. Diaphragm forming is a process that allows for “non-superelastic” alloys to be formed. The non-superelastic material is “hugged” over the mold using a combination of a sheet of heated “superelastic” aluminum and air pressure.

–  Complex forms can be created within a single component.

–  A range of sheet thicknesses can be used.

–  Can create subtle details and forms, without spring-back issues.

–   Limited to aluminum alloys.